Upload new Document while personalizing Sequence or Template send

My company often sends invoices, specifications, or finishes of our products via email with an attachment. This changes on a per client basis. We would like to be able to attach documents to a template or sequence in the editing phase right before sending.

None of the solutions mentioned previously worked for me, but I found a somewhat easy workaround solution. Upload the image to https://imgbb.com/ then copy the HTML code and paste it where you want the image in the sequence. This has worked for me every time and is relatively easy to do in bulk with many images/sequences!

We would like to add the comprehensive quote (pdf) as a document rather than an attachment. This allows us to then review when the document has been opened and how long the contact is spending on each page reviewing our proposal.

The current process is quite long winded. Once we have produced the quotation, we have to upload it to documents first and then go into quote templates and edit the template and search for the relevant document to add in.

Ideally we would like to be able to upload the document via our template directly from our server to streamline the process much quicker.